Novak Djokovic made a blistering return to form as Serbia reached the final of the Hopman Cup at Perth Arena.

Djokovic was below his best in a loss to Australia's Bernard Tomic earlier in the round-robin stage but he demolished Germany's Tommy Haas 6-2, 6-0 before Ana Ivanovic defeated Tatjana Malek 6-0, 6-1 as Serbia finished top of Group A.

Australia needed a German victory for any hope of qualifying for Saturday's final.

The world number one needed just 62 minutes to beat Haas, hitting 33 winners in his most impressive match of the week.

Djokovic and Ivanovic will meet the Spanish team of Fernando Verdasco and Anabel Medina Garrigues in the final.

"It's great. I came out on court today feeling much fresher than the opening few days," Djokovic said.

"I'm glad I could get a point for Serbia.

"Tommy's a very talented player. He's been struggling with injuries for the last few years.

"He's very persistent to come back into the top 10. I wish him all the best for the Australian Open."

Earlier on Friday, South Africa beat France 2-1 in their dead rubber when Jo-Wilfried Tsonga had to retire in the deciding mixed doubles because of a groin injury.

Chanelle Scheepers beat France's Mathilde Johansson 4-6, 6-4, 6-4 before Tsonga defeated Kevin Anderson 7-6 (7-4), 7-6 (7-3) during which the French player appeared to slightly injure his groin while stretching for a shot during a rally.

Scheepers and Anderson won the first set of the mixed doubles 6-3 and were trailing 2-1 in the second when Tsonga indicated he could not continue.

Tsonga then announced his withdrawal from the Sydney International, which begins on Sunday. The Australian Open gets underway on January 14.